1. Field of the Invention
This invention relates to a bit designed for drilling through rock and other hard surfaces, for example as used in drilling oil wells, etc. More specifically, it relates to a drill bit comprising an inner core or mandrel and an exterior sleeve or shell adapted to fit over the extreme lower end of the core. Still more specifically, the device of this invention may be fabricated from previously used or new bits.
2. State of the Prior Art
Drill bits are known and presently used which have carbide "compacts" deposited in openings in the lower exterior surface of the bit to provide hard grinding and chipping surfaces. Moreover, such bits are provided with linear openings therein through which air and/or liquid may be delivered to the areas being drilled to blast away dust and cuttings. Such drill bits are illustrated by those described in U. S. Pat. Nos. 2,725,216 and 3,185,228.
However, the carbide compacts used in such bits become worn and are thereby rendered inefficient or useless in the drilling operation, particularly in the outer areas of the bottom of the bit where the rotational speed of the bit is the greatest because this area is farthest from the axis of rotation. Therefore once these compacts are rendered inefficient for drilling purposes, even if only in the described outer areas, the complete bit must be discarded and replaced.